Ovarian Endocrine Activity: Role of Follistatin, Activin, and Inhibin

The first evidence of a testicular non-steroidal factor able to regulate the activity of the pituitary gland was reported by Roy McCullagh in 1932 [1]. He observed that the administration of an aqueous testicular preparation to castrated rats was able to restore the physiological characteristics of pituitary cells that had been altered after castration. This bioactive factor was called “inhibin.” When FSH and LH were purified, standards were available and specific radioimmunoassays were developed to determine their levels in biological fluids. The application of these methodologies to patients with gonadal dysfunctions confirmed the existence of a gonadal regulatory mechanism specific for FSH secretion. In adult males with damaged seminiferous tubules epithelium, a marked increase of FSH levels, concomitantly with normal testosterone and LH levels, was reported [2]. Similar observations were described in pre-menopausal women, with elevated serum FSH levels and normal estradiol, during the follicular phase of the menstrual cycle [3].